Pneumonia is the leading infectious cause of hospital admission and death in the United States. Streptococcus pneumoniae is the main bacterial cause of pneumonia and current vaccination programs aim to prevent serious pneumococcal disease and limit the disease burden. Pneumococcal polysaccharide vaccines, mainly used for adults, are efficacious in the prevention of invasive diseases, but its uptake is suboptimal and its effectiveness against pneumonia remains controversial. In 2000, a 7-valent pneumococcal conjugate vaccine was approved for use in young children and included in the U.S. infant immunization schedule. Post-licensure surveillance has shown dramatic reductions in rates of invasive disease in vaccinated children and older age groups. However, invasive pneumococcal diseases are relatively rare compared to pneumonia. The impact of the pneumococcal conjugate vaccination program on pneumonia hospitalizations is yet to be determined. [unreadable] [unreadable] The evaluation of the impact of vaccination policies and programs is fundamental for the advancement of public health. To date, the evaluation of routine immunization of U.S. infants is incomplete. Most reports compared pre- and post measurements of disease frequency and healthcare utilization in selected settings. None have taken into account the potential influence of secular trends and the lack of national data limited generalizability. Moreover, the effect of influenza and other winter virus activity was commonly unaccounted for. Interrupted time series analysis is the strongest, quasi-experimental design to evaluate longitudinal effects of implemented programs. They are particularly useful to control for secular trends and allow control for measurements of winter virus activity. [unreadable] [unreadable] This project proposes a formal evaluation of the pneumococcal conjugate vaccination program using data from the Nationwide Inpatient Sample (NIS) and the State Inpatient Databases (SID), the largest inpatient databases available for public use in the U.S. We will apply interrupted time series analyses to isolate the program impact from the influence of secular trends and will control for the influence of winter viruses, including influenza. This proposal will complement current program evaluation methodologies and includes designing a tool for future research by validating the use of NIS and SID for program evaluations and surveillance studies. We propose: 1) To examine changes in pneumonia hospitalization trends after the introduction of pneumococcal conjugate vaccines in selected NIS participating states and at the national level, using an interrupted time series analyses approach alone and accounting for the activity of respiratory winter virus. 2) To develop a reproducible methodology to monitor trends and evaluate interventions on this outcome as available information is updated. [unreadable] [unreadable] The potential of large databases for research is commonly underappreciated. We propose the use of NIS and SID for the evaluation of the pneumococcal conjugate vaccination program, using an innovative approach. [unreadable] [unreadable] [unreadable] [unreadable]